The crown region of a piston in an internal combustion engine is heated by the burning fuel air mixture. The piston, together with the piston rings, must effectively seal the combustion chamber against the passage of hot combustion gases and lubricating oil under all operating conditions. The trend to increase the specific output of internal combustion engines has resulted in the mechanical and thermal requirements of the engine pistons to also increase. The temperature of the piston in the area of the crown and ring grooves must remain within prescribed limits. At elevated temperatures the lubricating oil may gum the region of the ring grooves causing sticking of the rings, thus increasing blow-by, burnt rings, and possible seizure of the piston in the cylinder. Thermal cracks in the piston can also result if a maximum temperature is exceeded.
The most simple form of piston cooling is to spray the under crown of the piston with liquid coolant such as engine oil, however, for use in heavy duty internal combustion engines this method is not satisfactory since it will not dissipate sufficient heat.
A considerably more effective regulation of piston temperature is achieved by means of forced oil cooling of the piston. This method provides internal galleries or channels within the piston body in the area of the crown and ring and. Oil is force fed into the channel whereupon the oil will be shaken about in the channel by the piston motion. This turbulent "cocktail shaker" action results in the oil absorbing heat from the interior surface of the channel. Normally a jet arrangement directs cooling oil into the channel by way of a passage in the piston body connecting to the cooling channel. Likewise, oil exits the channel through a passage in the piston.
U.S. Pat. No. 4,651,631 issued to Jean-Claude Avezou on Mar. 24, 1987, U.S. Pat. No. 4,083,292 issued to Alex Goloff on Apr. 11, 1978 and U.S. Pat. No. 4,408,575 issued to Clairmont, Jr. et al. on Oct. 11, 1983 disclose piston designs where the cooling galleries are formed by the assembly of and the securing together of component parts. Such arrangements can be complicated and expensive to manufacture.
Normally in cast aluminum pistons the cooling channels are manufactured by casting in special shaped removable cores of various materials such as water soluble salt mixtures or graphite foam which can be burnt out. In some other arrangements the channels are formed out of sheet steel or cast-in pipe systems which remain in the piston. A problem with these types of arrangements is that the location of the gallery may not be the most desirable for maximum cooling because of structural considerations imposed on the piston by cyclic combustion gas loading and thermal growth. The void created by the channel may undesirably limit the fatigue strength of the piston or be responsible for initiating fatigue cracks. The providing, the placement, and the removal of cores to form the galleries add significantly to the cost to manufacture the piston. A mislocated core during the casting process can affect the balance of the piston and ultimately its performance.
It is the object of the present invention to provide a ring carrier assembly for a piston that defines a cooling channel through which liquid coolant circulates. With the cooling channel being integral with the ring carrier assembly improved cooling of the piston ring and crown areas is realized. Also with the cooling gallery being integral with the ring carrier assembly the structural integrity of the piston is maintained.
The present invention is directed to overcome one or more of the problems as set forth above.